The invention relates to a method for detecting and classifying helicopters by means of a radar system.
The detection of flying targets by means of radar surveillance systems is based essentially on the evaluation of the radial velocity of the flying object relative to the location of the radar system. With every revolution of the antenna, the target is covered for a period of less than about 50 ms and reflects a series of echo pulses which are evaluated by the radar signal processing system.
If a radial component is absent, as for example for tangential flight, the change in position from antenna revolution to antenna revolution is considered to be a flying target criterion.
Insofar as a helicopter performs similar movements, it is discovered and displayed by the radar system in the same manner as other flying targets. However, without further measures, the target cannot be classified as a helicopter, i.e. cannot be distinguished from other moving targets, as for example fixed wing aircraft.
One characteristic of helicopters which is particularly significant for combat helicopters, is their capability to be able to hover stationarily at a low height, thus eliminating the radial velocity component as well as the change in position for the detection process. The problem in this situation is to classify the helicopter as such in its environment of false targets (remnants of fixed target clutter, angels, road traffic, rain clutter).
In the interest of short sweep periods, and thus a high information renewal rate, the target dwell period, i.e., the time during which an individual target point is illuminated by the antenna lobe of the radar surveillance system, is usually less than 50 ms. Accordingly, the detailed evaluation of the spectrum of the target echoes or of the time curve of echoes from the same target is generally impossible.